Abstract

Calibrachoa La Llave & Lex. (Solanaceae) is a South American genus, comprised by 27 species, most of them ocurring in southern Brazil. The geographical distribution of related genera suggests an Andean origin, and the species are widely distributed in the Pampean region, with more abundant and concentrated occurrence in the highlands of Brazilian states of Parana and Santa Catarina. In Brazilian southeastern region, some disjunct populations of C. linoides were found, plus an endemic species (C ...

Calibrachoa La Llave & Lex. (Solanaceae) is a South American genus, comprised by 27 species, most of them ocurring in southern Brazil. The geographical distribution of related genera suggests an Andean origin, and the species are widely distributed in the Pampean region, with more abundant and concentrated occurrence in the highlands of Brazilian states of Parana and Santa Catarina. In Brazilian southeastern region, some disjunct populations of C. linoides were found, plus an endemic species (C. elegans) isolated at elevations above 1000 m. Another four species are also endemic, with few known individuals so far. This is the first study that used data from DNA sequencing in phylogenetic investigations in Calibrachoa, analysing cpDNA intergenic spacers trnH-psbA, psbB-psbH, trnL-trnF and trnS-trnG, as well as the trnL intron, in 25 of the 27 species considered. The two species not included in this study was C. felipponei e C. scabridula. In addition, a phylogeographical aproach was conducted from a larger sample set covering the majority of the geographical distribution of the assessed species. Ages for the main clades formed were also obtained, using the nucleotide substitution rate available for two spacers. The estimated age of the genus was 1.63 million years, and the speciation rate found is comparable to species of rapid radiation on islands. The phylogenetic trees obtained showed low bootstrap support values, and lack of resolution betwenn closely related species. The haplotype networks provided a more detailed relationship between species. These studies showed the occurence of ancestral sequences in morphologically different species. All these results pointed that Calibrachoa is a very recent genus, with high morphological divergence and low genetic differentiation. However, large genetic divergence was observed between the clade that includes C. parviflora and C. pygmaea, and the clade comprising the remainig species. Calibrachoa parviflora e C. pygmaea were quite distinct from other species. The ages presented showed that these clade diverged from to the rest about 500,000 years ago, a large period of time, when compared to the age of the genus. These results, together with other traits, suggest that these species could be regarded as a taxonomically distinct group of the remaining species. In relation to other species, the clades formed showed an association with geographical regions: the lowlands of Rio Grande do Sul and Argentina, and highlands in the region of Parana and Santa Catarina states. Another three groups were found, corresponding to endemic highlands species. The haplotype network also showed groups of related sequences, which reflected the clades found in the phylogeny. These results suggest that the large morphological differences found between species of the genus has occurred due to cycles of expansion and retraction of the grasslands and forest areas in the subtropical region of South America, changing the geographical distribution of Calibrachoa populations sereval times. These modifications in the landscape composition along repetitive climatic changes, were the result from glacial and interglacial cycles, which occurred at least nine times over the last million years. Moreover, evidences of possible recent expansions associated with the occurrence of natural hybridization between species were found, suggesting that, although environmental and ecological isolation exists between species, recent changes in the distribution of some species could cause the loss of these barriers. Additional studies, using rapidly evolving molecular markers, including other genomes, and more detailed investigations at the populational levels, can provide more complete information about the processes that led to this great morphological variation in a very short time. ...